Laser-sensitive drug seals blood vessels in a flash

点击量： 时间：2019-03-02 12:16:00

By Belle Dumé (Image: Nature/H Anderson) A way to close off diseased blood vessels with unprecedented accuracy using a zap of laser light has been tested in mice. The technique developed by Canadian, British and American researchers could be used to shut off blood vessels to treat certain tumours or a common eye disease. It is a significant upgrade to an existing treatment called photodynamic therapy (PDT), which involves injecting a light-sensitive compound into diseased tissue. Exposing the compound to laser light generates a high-energy form of oxygen that is toxic to cells. Using standard PDT, it is very difficult to focus the effect onto diseased cells without destroying adjacent healthy tissue. And the laser light needed can only penetrate 1 centimetre into the tissue. A new compound made by Harry Anderson and colleagues at Oxford University can tackle both those problems. Each molecule of the new drug is able to absorb two photons instead of just one, as for current PDT compounds. The drug displays a physical phenomenon known as two-photon excitation, which means much less energy is needed to perform the procedure. As a result, low-energy near-infrared light can be used, which can penetrate two or three times deeper into living tissue, depending on the particular tissue. That would allow many more uses for PDT. The process is also more accurate, explains Anderson. The underlying physics means the amount of two-photon excitation declines extremely rapidly with increasing distance from the focus of the laser beam. In tests on living mice, Brian Wilson of the University of Toronto, Canada, and colleagues, were able to close blood vessels with “exquisite spatial selectivity”, using pulses of laser light to “draw” along vessels they wanted to close. “The most immediate application is treating [advanced] age-related macular degeneration (AMD) by closing off unwanted blood capillaries,” Anderson told New Scientist. “It might also be used to treat certain tumours, particularly where improved accuracy is required.” The team will now go on to investigate the toxicology of the new photosensitive drug, and test its efficacy against tumours. “We are also experimenting with related compounds in an attempt to improve uptake by cells,” adds Anderson. “This paper is a breakthrough in two-photon PDT and I would mark it as in the top five important results for biophotonics in the past year,” commented David Cramb of the University of Calgary, Alberta, Canada, who also works on PDT. Attempts to make drugs capable two-photon excitation have faltered in the past, says Cramb. “There are many possibilities for this [new] technique – with the most obvious being for treating AMD.” Journal reference: